The way I think of it is my brain is a bit too busy to focus just on the text. I need to distract my motor brain, my visual brain and my repetitive tasks brain. Then my audio and informational brain can do their job without getting distracted. When I try to just listen or read the text my motor brain is sitting there idling and I have to keep using some attention to keep the breaks on or it will spin off into a ditch.
A interesting trick I have also found is reading in the bath. Something about being in the water makes my motor brain go into a dormancy mode where it doesn't interrupt.